METHOD FOR PRODUCING AN ELECTRODE POWDER MIXTURE FOR A BATTERY CELL

Abstract

The invention relates to a method for producing an electrode powder mixture for a battery cell. A powdered active material is provided with a powdered first polymer binder by means of electrostatic coating. The invention also relates to a method for producing an electrode of a battery cell.

Claims

1. A method for producing an electrode powder mixture of a battery cell, in which a powdered active material is provided with a powdered first polymer binder by means of electrostatic coating.

2. The method according to claim 1, wherein the powdered active material is provided with a powdered first conductive additive by means of electrostatic coating.

3. The method according to claim 2, wherein the first polymer binder is melted after the electrostatic coating.

4. The method according to claim 2, wherein the active material coated with the first polymer binder is mixed with a further binder.

5. The method according to claim 1, wherein a powdered second conductive additive is provided with a powdered second polymer binder by means of electrostatic coating and is then mixed with the active material coated with the first polymer binder.

6. The method according to claim 5, (38) the first polymer binder and the second polymer binder are melted before the mixing.

7. The method according to claim 1, (38) the grain size of the powdered first polymer binder is selected to be smaller than or equal to the grain size of the powdered active material.

8. A method for producing an electrode of a battery cell, in which an electrode powder mixture is produced according to a method for producing an electrode powder mixture for a battery cell according to claim 1 and the electrode powder mixture is applied to a conductor.

9. The method according to claim 8, (38) the electrode powder mixture applied to the conductor is heated and pressed and/or calendered.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In the following, embodiments of the invention are described in more detail with reference to the drawings, in which:

[0041] FIG. 1 is a schematically simplified view of a motor vehicle having a high-voltage battery with a plurality of structurally identical battery cells,

[0042] FIG. 2 is a side view of one of the structurally identical battery cells,

[0043] FIG. 3 shows a method for producing an electrode for a battery cell, comprising a method for producing an electrode powder mixture,

[0044] FIG. 4 shows a machine for producing the electrode powder mixture,

[0045] FIGS. 5-8 show greatly simplified and enlarged views of the electrode powder mixture at different stages of production,

[0046] FIG. 9 shows a further machine for producing the electrode,

[0047] FIG. 10 shows an alternative embodiment of the method for producing the electrode powder mixture, and

[0048] FIGS. 11-17 show greatly simplified and enlarged views of the electrode powder mixture produced according to the alternative embodiment at different stages of production.

[0049] Correspond parts are provided with the same reference signs in all figures.

DETAILED DESCRIPTION OF THE INVENTION

[0050] In FIG. 1, a motor vehicle 2 in the form of a passenger vehicle is shown in a schematically simplified manner. The motor vehicle 2 has a number of wheels 4, at least some of which are driven by means of a drive 6 which comprises an electric motor. Thus, the motor vehicle 2 is an electric vehicle or a hybrid vehicle. The drive 6 has a converter, by means of which the electric motor is powered. The converter of the drive 6 in turn is powered by an energy store 8 in the form of a high-voltage battery. For this purpose, the drive 6 is connected to an interface 10 of the energy store 8, which interface is introduced into a housing 12 of the energy store 8 which is made of stainless steel. A plurality of battery modules which are in electrical contact with one another are arranged inside the housing 12. Some of the battery modules are electrically connected to one another in series and these, in turn, are electrically connected to one another in parallel. The electrical assembly of the battery modules is in electrical contact with the interface 10 so that the battery modules are discharged or charged (recuperation) when the drive 6 is in operation. Because of the electrical interconnection, the electrical voltage provided at the interface 10, which is 400 V, is a multiple of the electrical voltage provided with the battery modules that are structurally identical to one another.

[0051] Each of the battery modules that are structurally identical to one another has a plurality of batteries that are structurally identical to one another and are electrically connected to one another in series and/or in parallel to form the specific battery module. Each of the batteries in turn has a plurality of battery cells 14 which are structurally identical to one another, two of which are shown here.

[0052] In FIG. 2, one of the structurally identical battery cells 14 is shown in a schematically simplified side view. The battery cell 14 has two electrodes 16 which are separated from one another by a separator 18. The two electrodes 16 and the separator 18 are stacked one on top of the other and are in direct contact with one another. One of the electrodes 16 is an anode 20 and the remaining of the electrodes 16 is a cathode 22.

[0053] The two electrodes 16 are constructed identically to one another and each have a conductor 24, which is also referred to as a carrier and is made of a metal foil. In the case of the anode 20, the conductor 24 is made of copper foil and in the case of the cathode 22 it is made of aluminum foil. A layer 26, the thickness of which is between 60 μm and 100 μm, is applied to both sides of each of the sheet-like conductors 24.

[0054] A method 28 for producing one of the electrodes 16 for the battery cell 14 is shown in FIG. 3. In the method 28 for producing the electrode 16, a method 30 for producing an electrode powder mixture 32 (FIG. 8) is first carried out. In a first working step 33, a powdered active material 38 is introduced through a filling opening 36 into a drum 34 shown in FIG. 4, a particle of the active material being shown in a schematically simplified view in FIG. 5. The powdered active material is tailored to the later use of the electrode 16 as anode 20 or cathode 22, and in this example it is graphite if the electrode is to form the anode 20. If the electrode 16 will form the cathode 22, the active material 38 LiFePO4 or NMC is used. The individual particles of the powdered active material 38 have a grain size of 1 μm, and to produce the powdered active material 38 a solid body is first ground in a method that is not shown in detail.

[0055] In a second working step 40, the (powdered) active material 38 is provided with a powdered first conductive additive 42 by means of electrostatic coating. For this purpose, a spray head 44 is arranged inside the drum 34, and by means of this the particles of the first conductive additive 42 are electrically charged and sprayed onto the particles of the powdered active material 38. The particles of the active material 38 are grounded via the metallic drum 34 so that the particles of the first conductive additive 42 are attracted to the particles 38 of the active material 38. During the electrostatic coating, the drum 34 is also rotated so that all particles of the powdered active material 38 are provided with at least one of the particles of the first conductive additive 42. Conductive carbon black is used as the first conductive additive 42, and as soon as one of the particles of the first conductive additive 42 has attached to one of the particles of the active material 38, the composite of these has a specific electrical charge, which prevents or at least makes more difficult/delays the attachment of further particles of the first conductive additive 42 until at least the same number of particles of the first conductive additive 42 have also attached to the majority of the remaining particles of the active material 38. Then there is no longer any difference between the charge of the composites produced in this way. Following this, attachment of a further particle of the first conductive additive 42 to the particles of the active material 38 is facilitated, so that the particles of the powdered active material 38 are coated essentially uniformly.

[0056] In a subsequent third working step 46, the powdered active material 38, the particles of which already have particles of the powdered first conductive additive 42 attached to them, is provided with a powdered first polymer binder 48 by means of the same spray head 44, namely also by means of electrostatic coating. In this process, the first polymer binder 48 also partially attaches itself to the particles of the first conductive additive 42 which are already adhering to one of the particles of the active material 38. The drum 34 is also rotated during the electrostatic coating. In a variant that is not shown in detail, a separate spray head is used to provide the powdered active material 38 with the powdered first polymer binder 48. The electrostatic coating also takes place by means of this separate spray head, and the separate spray head is also arranged inside the drum 34.

[0057] A fluoropolymer, namely polytetrafluoroethylene (PTFE) is used as the first polymer binder 48, and during spraying by means of the spray head 44, the drum 34 continues to rotate. The grain size of the powdered first polymer binder 48 is 200 nm and is therefore selected to be smaller than the grain size of the powdered active material 38. The grain size of the first conductive additive 42 is also selected to be between 100 nm and 500 nm and is therefore smaller than the grain size of the powdered active material 38.

[0058] In a subsequent fourth step 50, which is carried out when the electrostatic coating has ended, the first polymer binder 48 is melted. A light source 51 by means of which infrared light is emitted is arranged inside the drum 34 and is used for melting. In this process, as shown in FIG. 8, the individual particles of the first polymer binder 48, which are associated with the respective same particle of the active material 38 partially combine, so that the respective particle of the active material 38 is coated with the particles of the first conductive additive 42 adhering to it. In this way, the particles of the powdered active material 38 are also partially connected to one another by means of the first conductive additive 42. In one variant, the melting takes place by heating the drum 34, or the powdered contents of the drum 34 are emptied and moved through a continuous furnace.

[0059] In a subsequent fifth working step 52, the material produced in this way is mixed with a powdered further binder 54, which is also in particle form and whose particle size is between 500 nm and 800 nm. The further binder 54 is also, for example, polytetrafluoroethylene (PTFE) or, in an alternative embodiment, polymethyl methacrylate (PMMA), i.e. it is chemically different from the first polymer binder 48. The further binder 54 is merely poured into the drum 34 via the filling opening 36, with the drum 34 being rotated further so that mixing takes place. Subsequent to this, the method 30 for producing the electrode powder mixture 32 is ended. The fifth working step 52 is optional, and in a variant that is not shown in detail, the further binder 54 is not used.

[0060] In a subsequent sixth working step 56, the electrode powder mixture 32 created in this way is applied to both sides 24 of the respective conductor by means of electrostatic coating, as shown in FIG. 9. The conductor 24, which is also referred to as a carrier, is in the form of a metal strip that is unwound from a roll that is not shown in detail. Because the first polymer binder 48 has already melted, the particles of the first conductive additive 42 are held on the particles of the active material 38, so that the homogeneity of the electrode powder mixture 32 is retained even during the coating.

[0061] After the conductor 24 has been coated with the electrode powder mixture 32, it is heated and fed through a press 58, which is designed as a so-called “hot press” or “heat press”. By means of this press, pressure is exerted on the layers 26 in the direction of the conductor 24, so that the density of the electrode powder mixture 32 is reduced. For this purpose, any free spaces between the particles of the active material 38 are reduced or removed. Furthermore, heat is emitted by means of the press 58, so that the further binder 54 and the first polymer binder 48 are melted, which is why they bond to one another and to the first conductive additive 42 and the particles of the active material 38, so that the respective cohesive layer 26 is formed. A subsequent relative movement of the individual particles of the electrode powder 32 is thus prevented.

[0062] In a subsequent seventh working step 60, the conductor 24, which is provided with the layer 26 on both sides, is moved through a calender 62 which comprises two rollers 64. The layers 26 are further compressed by means of the calender 62 and their porosity is further reduced. It is also ensured in this way that the layers 26 have a predetermined thickness. The conductor 24 provided with the layers 26 is then rolled up onto a roll 66. If necessary, this is unrolled and cut to length to produce the respective electrode 16. In a variant that is not shown in detail, the press 58 is not present, and after the electrode powder mixture 32 has been applied to the conductor 24 by means of electrostatic coating, the conductor 24 is moved directly through the calender 62, the rollers 64 of which are heated, so that by means of this the further binder 54 and the first polymer binder 48 are melted and connected.

[0063] A variant of the method 30 for producing the electrode powder mixture 32 is shown in FIG. 10. This method begins with an eighth working step 68, in which first the powdered active material 38 is provided and introduced into the drum 34. Thus, in turn, there are a plurality of particles of the active material 38, one of which is shown in FIG. 11. Subsequently, the powdered active material 38, i.e. the individual particles of the active material 38, is provided with the powdered first polymer binder 48, namely individual particles thereof, by means of electrostatic coating, as shown in FIG. 12. The spray head 44 is used for spraying, and meanwhile the drum 34 is again rotated.

[0064] As soon as all particles of the active material 38 have been provided with sufficient particles of the first polymer binder 48, the first polymer binder 48 is melted so that the individual particles of the first polymer binder 48 adhering to one of the particles of the active material 38 fuse with one another and encase the particle 38, as shown schematically in FIG. 13. In other words, the eighth working step 68 corresponds to the first working step 33 and the third working step 46 and the fourth working step 50, whereby, however, the first conductive additive 42 is not present.

[0065] In a subsequent ninth working step 70, a powdered second conductive additive 72 is provided, of which two particles are shown in FIG. 14. This can again be conductive carbon black. The particles of the second conductive additive 72 are provided with a second polymer binder 74 by electrostatic coating. As a result, individual particles of the second polymer binder 74 attach themselves to the particles of the second conductive additive 72. For example, the same drum 34 from which the active material 38 was removed is used for electrostatic coating. However, it is also possible to use a machine of the same design, which also has a drum 34, or a machine of a different design. Subsequently, the second polymer binder 74 is also melted, so that the individual particles of the second conductive additive 72 are, for example, completely or at least partially connected to the second polymer binder 74, with a partially form-fitting connection and/or substance-to-substance bond being created between them. In summary, the eighth working step 68 corresponds to the ninth working step 70, but different materials are used. For example, the second conductive additive 72 is used instead of the active material 38 and the second polymer binder 74 is used instead of the first polymer binder 48. In one embodiment, the first polymer binder 48 and the second polymer binder 74 are chemically identical to one another. To summarize, the powdered second conductive additive 72 is thus provided with the powdered second polymer binder 74 by means of electrostatic coating.

[0066] In a subsequent tenth working step 76, the active material 38 provided, i.e. coated, with the first polymer binder 48 is mixed with the second conductive additive 72 provided with the second polymer binder 74, i.e. the specific coated powder, so that the electrode powder mixture 32 is formed, which is shown in FIG. 17. In this process, the first polymer binder 48 is connected with the second polymer binder 74, so that via this connection the particles of the active material 38 and of the second conductive additive 20 partially adhere to one another and consequently the electrode powder mixture 32 is homogeneous, and also remains so during storage.

[0067] The invention is not restricted to the embodiments described above. Rather, other variants of the invention can also be derived therefrom by a person skilled in the art without departing from the subject matter of the invention. In particular, all of the individual features described in connection with the individual embodiments can also be combined with one another in other ways without departing from the subject matter of the invention.

LIST OF REFERENCE SIGNS

[0068] 2 motor vehicle [0069] 4 wheel [0070] 6 drive [0071] 8 energy store [0072] 10 interface [0073] 12 housing [0074] 14 battery cell [0075] 16 electrode [0076] 18 separator [0077] 20 anode [0078] 22 cathode [0079] 24 conductor [0080] 26 layer [0081] 28 method for producing an electrode [0082] 30 method for producing an electrode powder mixture [0083] 32 electrode powder mixture [0084] 33 first working step [0085] 34 drum [0086] 36 filling opening [0087] 38 active material [0088] 40 second working step [0089] 42 first conductive additive [0090] 44 spray head [0091] 46 third working step [0092] 48 first polymer binder [0093] 50 fourth working step [0094] 51 light source [0095] 52 fifth working step [0096] 54 further binder [0097] 56 sixth working step [0098] 58 press [0099] 60 seventh working step [0100] 62 calender [0101] 64 roller [0102] 66 roll [0103] 68 eighth working step [0104] 70 ninth working step [0105] 72 second conductive additive [0106] 74 second polymer binder [0107] 76 tenth working step